Correct Answer - Option 1 : (a) only
The correct answer is option 1.
Distributed systems are using fixed routing whereas dynamic and virtual routing is not used in the distributed system.
Fixed routing: A path from A to B is specified in advance; the path changes only if a hardware failure disables it.
- Since the shortest path is usually chosen, communication costs are minimized.
- Fixed routing can not adapt to load changes.
- Ensures that messages will be delivered in the order in which they were sent.
Virtual routing: A path from A to B is fixed for the duration of one session.
- Different sessions involving messages from A to B may have different paths
- A partial remedy to adapting to load changes
- Ensures that messages will be delivered in the order in which they were sent
Dynamic routing: The path used to send a message from site A to site B is chosen only when a message is sent.
- Usually, a site sends a message to another site on the link least used at that particular time
- Adapts to load changes by avoiding routing messages on heavily used path
- Messages may arrive out of order
Hence the correct answer is (a) only.